1. Field of the Invention
The present invention relates to a torsion beam suspension configured so that both end portions of a torsion beam extending in a lateral direction of a vehicle are respectively bonded to a pair of lateral trailing members, each of which has a front end portion pivotally supported by a vehicle body and also has a rear end portion adapted to suspend wheels.
2. Description of Related Art
Hitherto, a related torsion beam suspension of an automobile has been configured so that both end portions of a torsion beam are welded to intermediate portions of the inner side walls of left and right trailing members (or arms), respectively (see, for example, Japanese Patent Unexamined Publications JP-A-10-230723 and JP-A-10-236123).
In such a torsion beam, due to unevenness of the surface of a road, on which the automobile runs, or to a lateral force caused during the turning of the automobile, trailing members supporting left and right rear wheels vertically swing with different amplitudes, respectively. Then, the torsion beam torsionally deforms due to the difference in vertical swinging angle between the left and right trailing members, so that a large stress is applied to a place at which each of both lateral ends of the torsion beam is welded to a corresponding one of the trailing members.
Thus, the strength of each welded portion is increased by increasing the anteroposterior width between both the lateral end portions of the torsion beam to increase the length of a part at which each of the lateral end portions of the torsion beam is welded to the corresponding one of the trailing members.
FIG. 7 is a partial cross-sectional view showing a welded portion of a related torsion beam suspension.
As shown in FIG. 7, the related torsion beam suspension 100 is configured v so that the top end portion 201 and the bottom end portion 202 of each of both the left and right ends of a cross-sectionally substantially-U-shaped torsion beam 200 opened to the front side of a vehicle are welded to the top surface and the bottom surface of a trailing member 300, respectively.
For example, when the trailing member 300 moves up and down, the torsion beam 200 is loaded with an upward bending moment A. An upper welded portion 210 has a very high stress concentration factor. Thus, a maximum stress is applied to this portion. Consequently, this portion may be peeled from the trailing member 300. Alternatively, a crack may occur in an end part of the welded portion 210.
Reinforcement measures against a stress applied to the connection portion between the torsion beam 200 and the trailing member 300 are, for example, a gusset provided at the connection portion, a notch formed in the connection part of the torsion beam, and a depression formed in the vicinity of the connection portion of the trailing member, as disclosed in the JP-A-10-230723 and JP-A-10-236123.
However, although the torsion beam suspensions as disclosed in the JP-A-10-230723 and JP-A-10-236123 are reinforced by the gusset or the depression against a horizontal bending moment, such countermeasures have no effect on the upward bending moment A caused when the trailing member 300 moves up and down, as shown in FIG. 7.
Thus, the related torsion beam suspensions have a problem in that the maximum stress due to the upward bending moment A is applied to the welded portion 210 to facilitate the peeling of the torsion beam 200 from the trailing member 300.
Generally, a method of changing the trimmed shape of each of both the left and right end portions of the torsion beam 200, a method of welding a reinforcement member over the welded portion 210, and a method of reducing the thickness of the torsion beam 200 are considered as means for solving this problem.
However, as shown in FIG. 7, the area of the top surface of the trailing member 300 is small. Thus, each surface, on which the torsion beam 200 is bonded to the trailing member 300, is restricted. Consequently, the method of changing the trimmed shape of each of both the left and right end portions of the torsion beam 200 is ineffective in solving the problem due to the bending moment A.
Also, the method of welding the reinforcement member over the welded portion 210 cannot have a large effect in dispersing a stress due to the bending moment A. This method has a problem in that the weight of the torsion beam suspension is increased due to the reinforcement member.
The method of reducing the thickness of the torsion beam 200 has a problem in that the stiffness of the torsion beam suspension 100 is decreased with reduction in the thickness thereof.
Thus, it is desired that the durability of the welded portion (joint portion) 210 of the torsion beam 200 against the bending moment A is enhanced without increasing the sizes of both the left and right end portions of the torsion beam 200 and without increasing the material cost and the welding cost of the torsion beam suspension 100.